Technical Field
Exemplary embodiments of the invention relate to a vehicle lamp for use in vehicles, etc.
Related Art
Previously, the mainstream of light sources of vehicle lamps, headlamps in particular, was halogen lamps and HID (high intensity discharge) lamps. However, in recent years, to replace those kinds of lamps, vehicle lamps using a semiconductor light source such as an LED (light-emitting diode) have been developed.
To increase the visibility further, light sources that employ a laser diode (also referred to as a “semiconductor laser”) and a phosphor instead of an LED have been developed (see JP 2004-241142 A, for example). In the technique described in JP 2004-241142 A, a phosphor is irradiated with ultraviolet light (excitation light) coming from a laser diode and thereby emits white light forward of the vehicle lamp. Thus, a predetermined light distribution pattern is formed. In the technique described in JP 2004-241142 A, the excitation light is not emitted forward of the vehicle lamp.
Another type of light source is known in which a laser diode generates blue excitation light instead of ultraviolet light. Receiving the blue excitation light, a phosphor emits fluorescent light whose spectrum is in a longer wavelength range (green to red) than the spectrum of the excitation light. The excitation light incident on the phosphor is scattered by the phosphor and loses coherence in passing through the phosphor. The phosphor outputs white light including scattered blue light and green-to-red fluorescent light.
For example, laser light sources are used for generating an additional high beam for illuminating a farther area than a high beam. FIG. 1 is a block diagram of a lamp system 1200 for generating additional high beams. A left lamp (vehicle lamp) 1300L and a right lamp 1300R are configured similarly to each other.
Each vehicle lamp 1300 includes a semiconductor light source (laser diode) 302, a lamp ECU 310, and a lighting circuit 320. The lamp ECU 310 is connected to a vehicle ECU 202 through a bus 203 such as a CAN (controller area network) or an LIN (local interconnect network).
A common power source (not shown) is used as a power source for a high-beam lighting circuit and a power source for the additional high-beam lighting circuit 320. A switch 312 of the lamp ECU 310 is disposed on a supply path of a battery voltage VBAT from a battery 204 to the lighting circuit 320. A CPU (central processing unit) 314 controls the turning-on/off of a high beam and an additional high beam by on/off-controlling the switch 312 based on an instruction, vehicle speed information, etc. supplied from the vehicle ECU 202.
To convey a sense of luxury, it is desirable that the light quantity of an additional light beam increase and decrease gradually with time, which is referred to as “gradual turning-on” and “gradual turning-off.” Gradual turning-on can be realized by utilizing a phenomenon that a constant-current converter 322 wakes up gradually when the switch 312 is turned on. On the other hand, as for the gradual turning-off, the output current of the constant-current converter 322 cannot be decreased slowly merely by turning off the switch 312.
Thus, the light circuit 320 includes a gradual turning-on/off circuit 324. The gradual turning-on/off circuit 324 performs gradual turning-on and turning-off by controlling the constant-current converter 322 according to a turning-on/off instruction signal S1 received from the CPU 314.